Japanese Patent Publication No. A2002-195331 discloses what has been proposed as a conventional mounting structure of a spring seat to this kind of a shock absorber.
This mounting structure, as shown in FIG. 7, is constructed such that a spring seat 46 receiving a suspension spring is inserted in an outer surface of an outer shell 45 constituting a shock absorber body 40 and the spring seat 46 is secured in a predetermined position thereto. The spring seat 46 is formed of a seat body 42 having a insert bore 41 into which the outer shell 45 is inserted and a flange-shaped seat portion 43 extending in the outer direction of the seat body 42 where both the spring seat 46 and the outer shell 45 are secured to each other by fitting a circular bulged portion 44 formed in the outer shell 45 into the insert bore 41.
In this case, the bulged portion 44 is formed by bulge machining. Namely the circular bulged portion 44 is formed by enlarging the outer shell 45 from an inside of the outer shell 45 toward an outer diameter direction thereof by a tool, and as a result the bulged portion 44 has a circular cross section for reason of machining.
Therefore, when the insert bore 41 of the spring seat 46 is pressed into the bulged portion 44 of the outer shell 45, a force in the direction shown by the arrow X, that is, the force which reduces the outer shell 45 in diameter acts as a component force. The force in the same direction with the component force is produced likewise in case a load is applied on the seat portion 43 of the spring seat 46 due to compression of the suspension spring where the suspension spring is installed to the shock absorber and operates as force which reduces the outer shell 45 in diameter as described above.
Since this force acts as a force which is likely to deform the outer shell 45 inside, that raises the problem with strength of the outer shell 45 in the event of reducing it in thickness. Namely, the structure of the bulged portion 44 makes reduction in thickness of the outer shell 45 difficult.